> From: [email protected]
> Subject: Galvanic Series in IEC950
> Date: Wednesday, October 01, 1997 7:34 PM
>
> Fellow Colleagues;
>
> Where is the authoritative reference/source of the galvanic potentials
> (electrochemical potential)? (normative annex J, section 2.5.10)
>
> I have looked in my CRC of Chemestry and Physics but could not
> decipher the electrochemical series (D-111) and my resulting voltage
> values differed by quite a bit. Also, a famous conductive gasket
> manufacturer lists the galvanic voltages which also differ from both
> the IEC and the CRC!
>
> Hans Mellberg
Hi Hans,
I *think* you may want to look into half-reaction
tables for the elements. Alloys will of course
appear differently. Let's take an example of
two elements in the galvanic table.
According to my old chemistry book,
Name Half-Reaction Potential
------ -------------------------
Iron Fe++ + 2e- = +0.440 volts
Copper Cu++ + 2e- = -0.345 volts
The Iron half reaction has a more positive
emf, therefore it proceeds as written.
The Copper half-reaction has a more negative
emf, therefore it will proceed from right
to left as written.
The total emf of the full reaction is
the algebraic difference of the two
half reactions involved.
The full reaction is
Fe = Fe++ + 2e- (Reduction)
Cu++ + 2e- = Cu (Oxidation)
-----------------------------------
Cu++ + Fe = Fe++ + Cu (Full Reaction)
The electrons cancel and the full reaction
proceeds as shown.
The total emf is 0.440 - (-0.345) = 0.785 volts.
Worst case it to 0.8 volts to be safe?
Table J.1 in UL-1950 3rd Edition says basically
Copper and Iron is about 0.8 volts.
In other words, take an iron nail and drop
it into a solution of Copper Sulfate CuSO4.
The *nail* will dissolve and the copper will
plate to the nail (precipitate out).
Take a strip of copper and drop it into
a solution of Ferrous Sulfate FeSO4.
Nothing will happen.
